Present experiments will be continued in order to determine the chronic effects of small concentrations of the pollutant gases NO2 and O2 on the metabolism of rats and mice. Animals will continue to be exposed, continuously throughout their life span to one of the following concentrations of these gases: 0.45 ppm NO2, 0.95 ppm NO2, 0.15 ppm O3, 0.45 ppm O3. The following parameters of response will be determined: (a) gross and histopathology of tissues and organs (b) growth rate (c) reproductive performance (d) longevity (e) concentration of lipofuscin age pigments in the tissues (f) levels of conjugated dienes in the tissue lipids (g) rate of oxidation of vitamin E in vivo (h) peroxidase activity in the tissues (i) methemoglobin formation in blood (j) changes in fatty acid distribution in the tissues (k) vitamin A oxidation in tissues. The effect on the susceptibility of the animals to these oxidants of depriving them of the natural lipid antioxidant vitamin E, of providing them with high levels of this vitamin and of administering the synthetic antioxidant DPPD, also will be determined.